Abstract: Air is removed from wood chips, and they are impregnated by treatment liquid, in a process that is an alternative to presteaming and is particularly applicable to environments where presteaming is undesirable, such as in the sulphite treatment of chips during the production of mechanical pulp. The chips are passed in a continuous manner in a generally serpentine, vertically oriented path so that the chips are subjected to a pressure build-up pulsation as they move downwardly, and a pressure release pulsation as they move upwardly. The diameters or cross-sectional areas of the conduit portions defining the upward and downward portions of the path are controlled so that there is about twice the residence time during pressure build-up than there is during pressure release. A high pressure feeder and pump with a fly wheel are operatively connected to one end of the serpentine path, while an in-line drainer and other apparatus are connected to the other end.